(1) Field of the invention
The present invention relates to an activated carbon and a production process thereof, and more particularly, to an activated carbon, having a large cation exchange capacity (i.e., capacity of substituting bases, and to be referred to as CEC, hereinafter) and excellent in fertilizer retention and a production process thereof.
(2) Description of the Prior Art
Activated carbon is a porous carbonaceous substance having a large surface area and large adsorption ability and has a wide range of uses as an adsorbent for various purposes.
Specifically, activated carbon can be used for adsorbing gases and vapors, recovering solvents, purifying and deodorizing gases, disposal of waste water, and decolorizing and purifying solutions. Further, activated carbon can be used as supports for catalysts.
Activated carbons have been manufactured by treating wood or brown coal with an activating agent, e.g., zinc chloride, phosphoric acid and the like followed by dry distillation, alternatively, by activating charcoal with steam. For example, charcoal, coconut husk, and the like are sufficiently carbonized followed by a high temperature treatment by means of steam. Or the activated carbon is activated by soaking in zinc chloride and calcinated at a high temperature.
The thus produced activated carbon typically has specific surface area of 800 to 1200 m.sup.2 /g, pore volume of 0.2 to 2 cm.sup.3 /g and pore size of 1 to 4 nm.
Activated carbon is mainly composed of carbon and includes small amounts of hydrogen, oxygen and inorganic components. With regard to the chemical structure, activated carbon is mainly composed of amorphous graphite and has functional groups such as hydroxy group, quinone group and the like on the surface.
Meanwhile, a typical activated carbon has a CEC or a capacity of substituting bases of about 1 to 7. CEC is represented by milligram equivalent (ME), which is a figure of expressing what milligram equivalent of bases a 100 g soil can retain, and CEC is used in the agriculture to indicate fertilizer retention ability in soil. That is, since, fertilizer components are generally composed of bases, the larger the CEC of soil, the more the soil can adsorb and retain fertilizer components. Therefore, the soil having a large CEC is capable of supplying fertilizers to crops continuously.
Accordingly, by utilizing the adsorbability of activated carbons, some activated carbons have been tried to be used as a fertilizer retaining agent to be compounded in a soil together with fertilizers. Nevertheless, the conventional activated carbons do not have a very high CEC (capacity of substituting bases), any particular result to be referred to has not been found.
Further, particle size of the activated carbons produced in conventional production process varies largely. For example, to prepare activated carbon graded in a particle size of 100 mesh, a considerable number of classifying steps would be needed so that the preparation was too complicated.
Meanwhile, in recent years, scrap tires as one of the industrial waste have increased largely in the amount and will be increased further with the spread of automobiles.
With regard to disposal of these scrap tires, various methods were already proposed in which scrap tires are burned as a fuel for a boiler for burning scrap tires so that the generated heat or heat energy may be utilized effectively to supply hot water, which in turn is used for bath, cooking and kitchen work, heating room and the like as occasion demands. These proposals are disclosed for example in Japanese Utility Model Application Laid-Open Sho 54 No. 58,658, Japanese Utility Model Application Laid-Open Sho 54 No. 161,644, Japanese Patent Application Laid-Open Sho 58 No. 26,914. Among them, specific features of these proposals are different with each other, nevertheless, any of these is oriented only to burn the scrap tires effectively and to utilize the generated heat efficiently, and no reference is found to formation of activated carbon.
On the other hand, the present inventors hereof noted that scrap tires as one of industrial wastes had increased largely in the amount with the recent spread of automobiles. That is, formerly, the scrap tires were burned only to heat water, but the present inventors previously found that activated carbon of good quality could be obtained when scrap tires were burned in a reformed and improved process of burning scrap tires. Namely, the present inventors proposed a technology in Japanese Patent Publication Hei 3 No. 79,608 which discloses a relatively simple configuration capable of obtaining an activated carbon of good quality from the cinder of scrap tires, and still providing an improved heat efficiency. This technology has been registered as Japanese Patent No. 1,709,953.
Now, the technology previously proposed by the present inventors will be described with reference to a perspective, partially cutaway view shown in FIG. 1.
In FIG. 1, reference numeral 1 designates a boiler for burning scrap tires. The boiler is constructed by a boiler body 2, a furnace floor 3 and a boiler outer casing 4 which is composed of front and backside walls 4A, side walls 4B and top plate 4C so as to enclose a space over furnace floor 3.
Outer casing 4 is divided into two rooms, i.e., an upper room 6 and an ash collecting room 7 by a lattice partition 5 spread over and spaced a predetermined distance from furnace floor 3. It should be noted that wall 25a of the ash collecting room 7 is formed by laid bricks.
Further, upper room 6 is constructed by a combustion chamber 8 disposed at lower portion thereof and an upper water chamber 9. Formed on the periphery of the side wall of combustion chamber 8 is a lower water chamber 10 that communicates with upper water chamber 9.
Reference numeral 8A designates a tire charging port opened in the front of combustion chamber 8. A lid 8B that can be opened and closed is provided for tire charging port 8A.
Reference numeral 7A designates an ash extracting port opened in the front of combustion chamber 8. A lid 7B that can be opened and closed is provided for ash extracting port 7B.
An upper combustion chamber designated at 11 is formed in the front portion of the above-mentioned upper water chamber 9. The chamber 11 communicates with combustion chamber 8.
An appropriate number of water tubes designated at 12 are disposed obliquely inside combustion chamber 8. The front ends of the tubes 12 are connected with the front portion of lower water chamber 10. The rear ends of tubes 12, disposed lower than the front ends, are connected with the rear portion of lower water chamber 10. Accordingly, waste heat including flame and heat in combustion chamber 8 is exhausted while heating water tubes 12.
A proper number of furnace tubes designated at 13 are disposed inside upper water chamber 9. The front ends of furnace tubes 13 communicate with upper combustion chamber 11 while the other ends are opened on backside wall 4A.
Reference numeral 14 designates an air jacket, which is additionally attached onto side wall 4B of boiler outer casing 4 in a position corresponding to combustion chamber 8. Air jacket 14 is communicated with combustion chamber 8 through lower water chamber 10 by a pertinent number of blast tubes 14A.
Reference numeral 15 designates a duct that communicates with air jacket 14. A blower 22 is jointed to duct 15. Air supplied to combustion chamber 8 is drawn in by blower 22, and blown into combustion chamber 8 through duct 15 and air jacket 14.
An exhaust pipe designated at 16 is provided in the upper portion of front wall 4A in boiler outer casing 4 so as to communicate with upper combustion chamber 11. An explosion-proof lid 16A is provided to exhaust pipe 16.
Reference numeral 17 indicates an exhaust chamber, which is additionally provided in the upper portion of backside wall 4A in boiler outer casing 4 so as to enclose the backside openings of furnace tubes 13. Exhaust chamber 17 is jointed with an exhaust gas tube 18, which in turn is jointed to dry type dust collector 19. Dust collector 19 is joined with a dust banker 20. This dust banker also communicates with exhaust chamber 17 through a fan 21.
In this case, the inside structure of dry type dust collector 19 is configurated as shown in a schematically illustrative sectional view in FIG. 2. Specifically, referring to FIG. 2, a baffle plate 30 is disposed inside dust collector 19 with a clearance 31 kept from the device wall. By this arrangement, suction air from a branch tube 18A flows as shown by arrows to generate a vortex flow to collect dust.
When scrap tires are burned in the thus constructed boiler, broken pieces of metal wires and activated carbon of good quality are accumulated as a cinder in ash collecting room 7. Therefore, it is possible to obtain activated carbons of different particle sizes by removing metal component by means of a magnet, etc., and classifying the residue using sieves.
The technology proposed previously by the present inventors is constructed as described heretofore.
As has been described, various kinds of boilers for burning scrap tires have been proposed, but there is yet room for further improvement, more or less for each of these proposals. With regard to the previously proposed technology by the present inventors, it is also desirable to make necessary improvements in order to further enhance the efficiency.
Boilers for burning scrap tires including the above-exemplified methods disclosed in the known articles are all constructed with blast tubes disposed under the lattice partition, or in upper portion of the combustion chamber, in order to enhance the efficiency of combustion. This structure suffers from the following drawbacks.
That is, in a case where the blast tubes are disposed under the lattice partition, the furnace inside wall is deteriorated by radiation heat generated by the combustion in the combustion chamber. To avoid this, an upright plate would be provided as a measure to protect the furnace inside wall from the radiation heat. But, this measure gives rise to new troubles, that is, the provision of the upright plate requires extra steps for the attachment and the installation becomes complicated.
On the other hand, when the blast tubes are disposed in upper portion of the combustion chamber, the blast tubes are directly exposed to flame of the combustion. Consequently, the tubes are deteriorated in a short period and must be replaced more frequently.
The technology proposed previously by the present inventors is to improve the above prior art method. Accordingly, the previously made proposal can provide a combustion system excellent in durability with a relatively simple configuration. The method further provides a good heat efficiency and a production of an activated carbon of good quality.
Nevertheless, the recent increase in the amount of scrap tires demands a further improvement of the processing efficiency in the disposal installation. Still more, as demand for the activated carbon of good quality obtained by the scrap tire disposal becomes larger, the production yield is desired to increase. For this reason, further improvement is desired also for the installation proposed previously by the present inventors.